The present invention relates to an iron silicide sputtering target having transition-type semiconductor characteristics and suitable for forming a βFeSi2 thin film to be used as an optical communication element or solar battery material, and the manufacturing method of such iron silicide sputtering target.
Although silicon has been the most popular material conventionally as the LSI semiconductor material, a compound semiconductor of indium/phosphorus, gallium/arsenic or the like is being used for optical communication (LE/LED).
Nevertheless, indium has an extremely short life span as a resource, and it is said that it can only be mined for another 20 years or so. Further, arsenic is well known as an element having strong toxicity. Thus, there is no choice but to say that the optical communication semiconductor materials being widely used today have significant problems for use.
In particular, the semiconductor element of gallium/arsenic being used in cell phones with a short product-life cycle includes arsenic having strong toxicity, and this is causing a significant problem regarding the waste disposal thereof.
Under the foregoing circumstances, it has been discovered that βFeSi2 possesses transition-type semiconductor characteristics, and is being noted as a favorable optical communication element and solar battery material. The greatest advantage of this βFeSi2 is that the respective constituent elements are extremely abundant on earth, and that there is no danger of toxicity or the like. Thus, these materials are known as environmentally friendly materials.
Nevertheless, this βFeSi2 is not free of problems, and, at present, technology for preparing high-quality material comparable to compound semiconductors of indium/phosphorus, gallium/arsenic or the like has not yet been established.
Currently, as technology for forming an FeSi2 thin film, proposed is technology for forming βFeSi2 by sputtering an Fe target and forming an Fe film on a Si substrate, and thereafter generating a silicide formation reaction between Si as the substrate material and the Fe film by heating the deposited Si substrate.
Nevertheless, there are problems in that, with this method, since the substrate needs to be heated at a high temperature for a long period during deposition and during annealing, there will be limitations on the device design, and that it is difficult to form a thick βFeSi2 film since the silicide formation reaction is based on the diffusion of Si from the substrate.
As a method similar to the above, proposed is a method of accumulating Fe on the Si substrate while maintaining the substrate at a temperature in which Fe and Si will react; that is, at 470° C., but this method also encounters problems similar to those described above.
Further, as another method, proposed is a method for forming a βFeSi2 film by separately sputtering the Fe target and Si target; that is, performing co-sputtering so as to laminate several layers of the Fe layer and Si layer, and heating this to generate a silicide formation reaction.
Nevertheless, with this method, there are problems in that the sputtering process will become complex, and that it is difficult to control the uniformity of the thickness direction of the film.
Each of the foregoing methods is based on the premise of performing annealing after depositing Fe on the Si substrate, and, with these methods that require heating at high temperatures for a long period, a problem has been noted in that the βFeSi2, which was formed in a film shape, becomes aggregated into an island shape together with the progress of annealing.
Further, with the foregoing methods, since the Fe target is a ferromagnetic body, it is difficult to perform magnetron sputtering, and it is thereby difficult to form an even film on a large substrate. Therefore, an even βFeSi2 film with few variations in the composition resulting from the subsequent silicide formation could not be obtained.
Moreover, although a proposal of a target (mosaic target) in which Fe and Si blocks are disposed in a prescribed area ratio has also been made, since the sputtering rate of Fe or Si, whichever is sputtered, will differ considerably, it is difficult to deposit a prescribed film composition on a large substrate, and it was not possible to prevent the arcing or generation of particles at the bonding interface of Fe and Si.
Conventionally, as technology employing FeSi2, technology relating to the manufacturing method of a thermoelectric material including the steps of forming capsule particles by covering the nuclear particles of FeSi particles with Si particles of a prescribed weight ratio, performing current-conduction sintering to the powder aggregate of the capsule particles, and generating an FeSi2 intermetallic compound has been disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. H5-283751).
Further, a manufacturing method of βFeSi2 including a step of pulverizing and mixing raw material powder containing Fe powder and Si powder, a step of molding the pulverized and mixed powder, and a step of sintering the molded material has been disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. H6-81076).
Moreover, a manufacturing method of iron silicide thermoelectric material including the steps of mixing ferrosilicon and iron powder, and subsequently performing pressure sintering thereto at a sintering temperature of 900 to 1100° C. under an inert atmosphere has been disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. H7-162041).
Further, a manufacturing method of raw material powder for an FeSi2 thermoelectric conversion element including the steps of mixing a prescribed amount of transition metal powder to fine powder obtained via jet mill pulverization with inert gas so as to easily obtain fine powder having a low residual oxygen content and an average grain size of several μm or less, performing spray granulation thereto with a spray dryer, and subsequently performing pressing and sintering thereto has been disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. H10-12933).
Moreover, a metallic silicide luminescent material in which a β-iron silicide semiconductor element, which is a metallic silicide semiconductor particle having a grain size on the order of nanometers, is dispersed in a particle shape in the polycrystalline silicon has been disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. 2000-160157).